Macromolecules 2000, 33, 3999-4007
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Synthesis and Characterization of Phosphazene Di- and Triblock Copolymers via the Controlled Cationic, Ambient Temperature Polymerization of Phosphoranimines Harry R. Allcock,*,† Scott D. Reeves,†,‡ James M. Nelson,†,§ and Ian Manners| Department of Chemistry, The Pennsylvania State University, 152 Davey Laboratory, University Park, Pennsylvania 16802; and the Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario M5S 1A1, Canada Received November 9, 1999; Revised Manuscript Received March 2, 2000
ABSTRACT: An advanced process for the synthesis of polyphosphazenes with controlled architectures has been investigated. By this method, a wide range of well-defined phosphazene di- and triblock copolymers with controlled molecular weights and narrow polydispersities have been synthesized (Mn up to 4.8 × 104 with polydispersities of 1.06-1.39). The diblock copolymers, {[NdPCl2]n[NdPR(R′)]m}, were synthesized by the cationic condensation polymerization of the phosphoranimines, PhCl2PdNSiMe3, Me(Et)ClPdNSiMe3, Me2ClPdNSiMe3, Ph2ClPdNSiMe3, and PhF2PdNSiMe3, at 35 °C initiated from the “living” end unit of poly(dichlorophosphazene), [Cl-(PCl2dN)n-PCl3+PCl6-] which was itself formed by the polymerization of Cl3PdNSiMe3 with small amounts of PCl5 initiator in CH2Cl2 at 25 °C. Halogen replacement reactions through the use of NaOCH2CF3 and/or NaOCH2CH2OCH2CH2OCH3 on the diblock copolymers yielded fully organo-substituted macromolecules. In addition, the diblock copolymer {[Nd PMe(Et)]n[NdPMe(Ph)]m} was formed by the block copolymerization of the two different organophosphoranimines. Triblock species were produced by the reaction of the “living” difunctional initiator, -{CH2NH(CF3CH2O)2P-N-PCl3+PCl6-}2, first with Cl3PdNSiMe3 and second with Me(Et)ClPdNSiMe3, followed by halogen replacement with NaOCH2CF3, to yield the triblock {[(Et)MePdN]m[(CF3CH2O)2Pd N]n-P(OCH2CF3)2NHCH2CH2NH-(CF3CH2O)2P-[NdP(OCH2CF3)2]n[NdPMe(Et)]m}. The evidence for the formation of the di- and triblock copolymers includes NMR, GPC, elemental analysis, and solubility data.
Introduction Polyphosphazenes, (NdPR2)n, are inorganic-organic polymers in which the side group (R) can be halogeno, organo, or organometallic units. A large number of different polyphosphazenes are known, all with the same backbone structure but with different side groups attached to the phosphorus atoms of the skeleton. Different side units are normally introduced via the macromolecular replacement of the halogen atoms in poly(dichlorophosphazene), (NdPCl2)n, by organic groups using organic or organometallic nucleophiles. Two or more different types of side groups can be incorporated by sequential or simultaneous substitution reactions. These generate a wide range of property combinations that result from the presence of the inorganic backbone and the large number of side group permutations.1,2 A particular challenge in this field is to develop methods for the preparation of block copolymers that contain phosphazene units. Block copolymers offer the prospect of amphiphilic materials and macromolecules with controlled compatibility with other polymers as a route to the preparation of polymer alloys and interpenetrating networks, especially in combination with conventional organic polymers. Polyphosphazenes can be synthesized by a number of different methods. However, many of the polymerization routes allow little or no control over the molecular * To whom correspondence should be addressed. †The Pennsylvania State University. ‡ Current address: Midland Macromolecular Institute, Midland, MI. § Current address: 3M Corporate Research, St. Paul, MN 55144. | The University of Toronto.
weight (MW) and yield polymers with broad polydispersities (PDI). The widely used ring-opening polymerization of (NPCl2)3 produces polymers with high MWs (Mw∼106), but with a number of drawbacks, which include the high polymerization temperatures required to produce (NPCl2)n (210-260 °C), the absence of molecular weight or architectural control, and the high PDIs of the polymers (up to 10 in some cases).3 Other synthetic methods involve the condensation polymerization of organophosphoranimines. These reactions, with or without anionic initiators in the bulk state at 100-200 °C, have yielded polyphosphazenes with Mn values up to ∼105 and polydispersities of less than 3.4-11 Phosphazene block copolymers, such as {[NdP(OCH2CF3)1.16(OCH2CH2OCH3)0.84]n-[NdP(OCH2CF3)2]m} derived from the monomers (CF3CH2O)3PdNSiMe3 and (CH3OCH2CH2O)(CF3CH2O)2PdNSiMe3, have been synthesized by the thermal anionic copolymerization of these organophosphoranimines.12-14 This method yields block copolymers in which one of the blocks has random substituents because of the two possible leaving groups on one of the phosphoranimines (e.g., CH3OCH2CH2Oand CF3CH2O-). The block copolymers produced by anionic polymerization have Mn values up to ∼105, with PDIs of less than 2. Recently, an ambient temperature route to polyphosphazenes was discovered in our laboratories via the solution-state living cationic polymerization of halophosphoranimines initiated by small amounts of PCl5 (Schemes 1 and 2).15-18 For example, the monomer, Me3SiNdPCl3 can be polymerized to (NPCl2)n by this method. This new route has provided an improved method for the synthesis of polyphosphazenes with controlled molecular weights (Mn up to ∼105) with low
10.1021/ma991890+ CCC: $19.00 © 2000 American Chemical Society Published on Web 05/12/2000
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Macromolecules, Vol. 33, No. 11, 2000 Scheme 1
Scheme 2
polydispersities (
